Acoustic sensors operating in lossy environments, such as water, require significant sensitivity to overcome the sound attenuation in the environment and thus see farther. We show here that a surprisingly large class of passive fluids has the ability to enhance the sound pressure propagating inside them without employing active actuation. Specifically, the general requirements for this remarkable property are fluid impedance higher than the impedance of the environment and negligible insertion loss as sound propagates from the environment into the high impedance fluid. We demonstrate the pressure enhancing effect by designing a broadband isotropic metafluid that increases the pressure of sound waves impinging from water. We validate the design in numerical simulations showing that significant sound pressure level increases are achievable in realistic metafluid structures in large bandwidths covering several octaves. Our approach opens up unexplored avenues towards improving acoustic transducer sensitivity, which is critical in applications, such as medical ultrasound imaging, sonar, and acoustic communications.

中文翻译：

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被动元流中的宽带声压增强

在有损环境（例如水）中运行的声传感器需要很高的灵敏度，才能克服环境中的声音衰减，从而视线更远。我们在这里显示出令人惊讶的一大类被动流体能够在不采用主动致动的情况下增强在内部传播的声压。具体而言，对此卓越性能的一般要求是流体阻抗要高于环境阻抗，并且随着声音从环境传播到高阻抗流体中，插入损耗可以忽略不计。我们通过设计宽带各向同性的微流体来证明压力增强效果，该流体可以增加从水中撞击的声波的压力。我们在数值模拟中验证了该设计，结果表明，在覆盖数个八度音阶的大带宽中，在实际的元流体结构中可以实现显着的声压级增加。我们的方法为提高声换能器灵敏度开辟了未探索的途径，这在诸如医学超声成像，声纳和声通信等应用中至关重要。